Something remarkable is happening in California politics, but the leaders of the two major parties don’t seem to get it.

Voters are deserting the Republican Party in droves, but most are not going to the Democrats. Instead, they are declaring their independence and becoming an unpredictable force capable of moving elections one way in a particular year and reversing their field the next.

The same thing is happening nationally, but the California secretary of state’s voter registration report produced shortly before each statewide election demonstrates the phenomenon is at least as strong here as anywhere else.

Two recent election results reveal the enormous potential importance of what’s happening: When the large majority of decline-to-state voters swung Democratic in 2008, they handed the presidency to Barack Obama. But when the same category of voters went the other way in Massachusetts two months ago, Republican Scott Brown won the Senate seat held for more than 50 years by John and Edward Kennedy.

Here are the new numbers that essentially render California a swing state, one that neither party can afford to take for granted, even if some analysts persist in calling this a solidly “blue” Democratic state:

Democrats remain the largest party in this state, with about 7.5 million adherents, about 45 percent of all registered voters. Republicans are second with 5.2 million registered members, or 31 percent. There has been some increase among Democrats since the last statewide primary election in 2006, but most of that bump came during the Obama voter registration drive of 2008 and no one knows how many of those new voters will turn out again.

But decline-to-states are up almost 600,000 over the last four years, rising from barely 18percent of all voters to just over 20 percent. Anyone who doesn’t think 600,000 voters can swing an election hasn’t been paying attention.

And yet the leaders of both major parties continue to oppose the kinds of changes independents usually like and vote for.

It was a joint effort of both major party organizations that killed the “blanket” primary California used for a couple of years after voters approved it in 1996 by a 59-41percent margin. The two parties – which agree on few other things – also joined forces in 2004 to defeat an effort to set up a “top two” primary election system that would list all candidates together on the primary ballot, regardless of party, with the top two vote-getters advancing into the November runoff election.

A similar proposal will be on the ballot in June as Proposition 14, and once again the two major parties are working in tandem to defeat it.

They say they don’t like the measure because it would almost always take minor-party candidates like those of the Libertarian and Peace and Freedom parties off the runoff ballot. Translation: It could permit the decline-to-state voters and other moderates to break the monopoly now held by extreme conservatives and extreme liberals in the respective primaries of the Republican and Democratic parties.

With party registration tending to be heavily skewed in one party’s favor in most legislative and congressional districts, party nominations are now usually tantamount to election.

But, some say, decline-to-state voters can now participate in the primaries of both the Republicans and Democrats. That’s correct – but only if they specifically request a party ballot. How many voters even know such a request is possible and will be honored by election workers? And virtually no one knows how any decline-to-state who votes by absentee mail ballot can participate in either major party primary.

All of which means that the extremists now running the two major parties will likely keep control of district-based elections unless Proposition 14 passes. But decline-to-states have become so numerous that California might be back to unpredictable swing-state status from this fall forward, as they move back and forth.

Pass Proposition 14 and district-based elections might also become unpredictable again, something that could help bring an end to the uncompromising partisan paralysis that so often afflicts state government.